1. Field of the Disclosure
The present disclosure relates to processes for forming electronic devices, and more particularly processes for forming electronic devices that include a semiconductor layer.
2. Description of the Related Art
Electronic device substrates, including semiconductor device substrates, continue to increase in size. Currently, nominally 300 mm diameter substrates are used within the semiconductor industry. As device performance increases, device geometries, including thicknesses of layers, decrease. The ratio of wafer diameter to layer thickness increases, controlling some parameters, such as heat, reaction rates, etc., to be uniform across the entire surface of the substrate can be difficult.
FIG. 1 includes an illustration of a cross-sectional view of a workpiece 10 to better illustrate the problem. The workpiece includes a semiconductor device substrate 12, a buried insulating layer 14, and a semiconductor layer 16, which includes SiGe. Each of the buried insulating layer 14 and semiconductor layer 16 are initially formed to a substantially uniform thicknesses across the semiconductor device substrate 12. When performing a germanium condensation operation to enrich the germanium content within the semiconductor layer 16, an oxidation is performed and forms oxide layer 18. The oxidation rate on the wafer is dictated among other things by local mechanical stress and local temperature. Because of the wafer geometry, the heat can be dissipated more readily near the wafer edge. The same holds for the mechanical stress which will be differently distributed in the center than at the edge of the wafer. It is thought that the combination of stress and temperature effects is responsible for the nonuniform growth of oxide on the wafer. For the condensation operation, the thickness of the semiconductor layer 16 is thinner and has a higher concentration of germanium as compared to the semiconductor layer 16 near the edge of the workpiece 10. Such variations are undesired.
Note that the problem is not limited to just a germanium condensation operation. Other processing operations can be affected. Also, other types of electronic substrates, including flat panel display substrates, may experience similar affects during processing.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.